1. Field of the Invention
The invention relates to an irrigation valve device comprising a valve and a swellable member which controls the valve in response to its moisture content and is subjected to the water passing through the valve.
2. Description of the Prior Art
A known irrigation valve of this kind comprises a swellable member consisting of wood chips which are accommodated in an apertured cylinder and act on a magnetic valve. The magnetic valve is included in an irrigation conduit which feeds a lawn sprinkler. The latter is arranged so that the water sprayed from it reaches the horizontally disposed apertured cylinder and, through the apertures in the cylinder, the swellable member. When sufficient water has been absorbed, the swellable member closes the magnetic valve. For the purpose of regulating the flow of water to the swellable member, the periphery of the apertured cylinder has apertures which differ in number and diameter. By turning the apertured cylinder, a different total cross-sectional area is offered to the sprayed water so that the latter will contain more or less water at a given spraying intensity. One disadvantage of this irrigation valve resides in the fact that the apertured cylinder to a very large extent covers the swellable member from the outside and consequently the surrounding air does not have adequate access to the swellable member for the purpose of drying the same. As a result, there is a very long drying period during which no spraying can take place. In addition, the magnetic valve is either open or closed and thus in the open position of the magnetic valve an excessive supply of water must be offered to the plants so that the latter can withstand the period during which the magnetic valve is switched off. However, artificial irrigation is more rational and more effective if the water can be supplied with more continuity.
German Gebrauchsmuster No. 77 06 643 describes another irrigation valve device that works with a swellable member of wood which is accommodated in an apertured cylinder, has one end acting on a diaphragm valve and its other end supported against a screw-threaded plug. By screwing the plug into the apertured cylinder to a greater or lesser extent one can adjust the response threshold of this known hygrostat. Since this irrigation valve device is intended to be buried in the earth, adjustment of the response threshold of the valve by turning the plug is very cumbersome to start with because, since the plug is located at the lower end of the valve, it must be dug out of the earth completely. Further, adjustment of the play for the swellable member is basically inadequate to achieve optimum artificial irrigation because only the length of swelling is set at which the valve will close or open but one cannot, for example, vary the frequency of operation. Apart from the poor accessability of the plug for setting the response threshold, the installation of the hygrostat in the earth has the additional disadvantage that the swellable member cannot be dried out by the outside air. However, the dissipation of moisture by the wood to the earth is too slow for the irrigation of plants because, in contrast with a plant, the swellable member does not withdraw water from the earth and hence the earth in the vicinity of the wooden member remains moist for a longer period than in the region of a plant using up water. These long inoperative periods have to be compensated by correspondingly intensive irrigation of the plants during the operative periods of the valve, which is contrary to the aim of achieving a water supply that is as continuous as possible.
DE-AS No. 1 191 163 describes an apparatus in which the swelling of a swellable member in the form of a wooden rod pinches a water hose and thereby inhibits the supply of water to a plant container, the swellable member being subjected to liquid from the earth by way of a sponge in the base of the plant container. In this apparatus there is likewise a set screw for the play of the swellable member, with which one can merely set the degree of swelling of the swellable member at which the hose will be pinched shut.
DE-AS No. 1 039 296 describes an automatic irrigating apparatus for cultivated plants, in which a hygrometer at the end of a tube insertable in the earth controls a liquid valve disposed at the other end of the tube. The humidity threshold at which the valve is to be actuated can for example be regulated by a set screw. Again, this irrigating apparatus has inherent disadvantages resulting from the accommodation of the hygrometer in the earth.
A humidity-controlled valve of quite a different kind is disclosed in DE-OS No. 2 513 600. This known valve adapts the irrigation to atmospheric conditions, i.e. the valve remains closed during rain or very humid conditions and opens for a predetermined adjustable time interval when it is dry. The irrigating water passing through the valve is not returned to the swellable member.
A control device described in DE-OS No. 23 25 980 comprises a valve member in which the interior accommodates a swellable member acting on the valve seat and which has lateral apertures and a top aperture for the entry of water for swelling purposes. The valve member is placed on or in the earth. There is no provision for setting a particular control behavior of the device.
Finally, U.S. Pat. No. 3,512,712 describes an automatic irrigating apparatus that operates with a humidity sensor which is connected by way of a wick to the part of the earth to be watered and is otherwise subjected to the humidity of the air. The humidity film comprises a swellable member in the form of hollow cylindrical blocks of which the swelling is transmitted to an indicating apparatus and to an irrigating valve. The supply of water for swelling purposes from the earth to the swellable member cannot be controlled.